Analytical apparatus

ABSTRACT

Apparatus for determining the oxygen demand of combustible materials in aqueous dispersions and for determining the total carbon content of aqueous systems. The apparatus comprises a combustion tube surrounded by controlled heating means. The combustion tube has sample insertion means and reference gas including oxygen inlet means at an entry end, sample expansion zone and catalyst disposed within the tube, an oxygen detector cell disposed within the tube and gas outlet means coupled to the exit end of the tube. The gas outlet means is coupled to carbon dioxide detection means. Readout means are coupled to both detectors. The reference gas passes through a closed path in the oxygen detector prior to its insertion at the entry end of said combustion tube.

United States Patent [191 Pacth ANALYTICAL APPARATUS Primary Examiner-Morris O. W-olk [75] Inventor: William H. Parth, Saginaw, Mich. Assstam Serwm Attorney-William M. Yates et all. [73] Assignee: The Dow Chemical Company,

Midland, MlCh. [57] ABSTRACT [22] Flled: 1971 Apparatus for determining the oxygen demand of [21] App]. No.: 195,387 combustible materials in aqueous dispersions and for determining the total carbon content of aqueous systems. The apparatus comprises a combustion tube sur- P 23/253 b if y rounded by controlled heating means. The combustion [58] F id IIIII C ube has sample insertion means and reference gas in- 1e 0 earc, 232232 eluding oxygen inlet means at an entry end, sample expansion zone and catalyst disposed within the tube, an oxygen detector cell disposed within the tube and gas [56] References cued outlet means coupled to the exit end of the tube. The UNITED STATES PATENTS gas outlet means is coupled to carbon dioxide detec- 3,296,435 1/1967 Teal et al 23/230 PC X tion means. Readout means are coupled to both detec- ,064 3/ 1968 Kolsto tors. The reference gas passes through a closed path in zeal at all the oxygen detector prior to its insertion at the entry an a .1 3,679,364 7/1972 Teal et al 23/230 PC end of Sald f 9 Claims, Drawing Figures Readou/ ew'c e 60 12 f 817 R aofou/ 6 r i 9 3C EV/CE. 1 62 i I i 43 58 54 i I I: 2/? [I I r 6 M egg;

PATENTEUJMI 8 m4 SHEET 2 BF 2 Perm any/i0 r) 7 4/5 6 1 ANALYTICAL APPARATUS BACKGROUND OF THE INVENTION This invention relates to novel apparatus for determining the total carbon content of aqueous systems and the total oxygen demand of combustible materials in aqueous systems.

Apparatus presently in use for determining the total oxygen demand of combustible materials in aqueous dispersions is exemplified by the apparatus disclosed in Teal et al. s U. S. Pat. No. 3,560,156.

While such an apparatus is effective for its intended use, an external oxygen detector is used which requires a separate temperature controlled compartment, does not respond as fast as is desired, is susceptible to contamination, and whose operational freedom from maintenance could be improved. Further, the detector output may be affected by vibration.

Apparatus for determining the total carbon content of aqueous systems is disclosed and claimed in Teal et al. s U. S. Pat. No. 3,296,435, in which there is utilized a combustion tube and furnace similar to that used in Teal et al. US. Pat. No. 3,560,156.

Accordingly, a principal object of this invention is to provide an improved analytical instrument for determining the total oxygen demand of combustible materials in aqueous dispersions.

Another principal object of this invention is to provide an improved combination analytical instrument for determining both the total oxygen demand of combustible materials in aqueous dispersions and the total carbon content of aqueous systems.

Another object of this invention is to provide a faster responding instrument for determining the total oxygen demand of combustible materials in aqueous dispersions.

A further object of this invention is to provide an improved instrument for determining the total oxygen demand of combustible materials in aqueous dispersions which has low susceptibility to contamination.

Yet another object of this invention is to provide an improved instrument which is easy to operate and maintain.

STATEMENT OF INVENTION The invention is apparatus for determining the city gen demand of combustible materials in aqueous dispersions and for determining the total carbon content of aqueous systems. I

The apparatus comprises a combustion tube surrounded by controlled heating means. The combustion tube has sample insertion means and reference gas including oxygen inlet means at an entry end, sample expansion zone and catalyst disposed within the tube, an oxygen detector cell disposed within the tube and gas outlet means coupled to the exit end of the tube. The gas outlet means is coupled to carbon dioxide detection means. Readout means are coupled to both detectors. The reference gas passes through a closed'path in the oxygen detector prior to its insertion at the entry end of said combustion tube.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view, partly in section, of apparatus in accordance with this invention;

FIG. 2 is a fragmentary view of alternative means for supplying feed gas to the apparatus of FIG. 1;

FIG. 3 is an enlarged fragmentary view of the output end of the combustion tube showing the oxygen detector in place therein;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3, and

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 3.

Referring to the drawing, there is shown apparatus, indicated generally by the numeral 10, comprising a temperature controllable furnace 12 having an electri cal resistance heating winding 14 adjacent toan axial bore 16 extending from end to end of the furnace 12. The furnace I2 is conveniently of the same type and may use the same temperature control means as the electric furnace 9 in Teal et al., U. S. Pat. No. 3,560,156.

A combustion tube 68, indicated generally by the numeral 18, is disposed within the axial bore 16. The combustion tube 68 is a gas impermeable, elongated hollow element made of quartz, for example, and whose ends are closed during operation.

The so-called entry end 88 of the combustion tube 68 is closed by a sample insertion means (illustrated as a syringe 90, for example, and reference gas inlet header 92, which accepts the syringe 9t) and accepts reference gas from the tube 42 coupled thereto.

the output end 94 of the combustion tube 68 is closed by a header 26 having an oxygen detector assembly 24 extending into the tube 67.

The header also has a reference gas inlet bore 95, a reference gas exit bore 44, each communicating with the detector assembly 24, a vent bore 46 communicating directly with the combustion tube 68, and means for coupling electrical leads 48, 50 to the detector assembly 24 (see FIG. 3). i i

The header assembly has a cylindrical part which extends into the tube 68 and an O ring 82 which effects a seal therebetween The leads 48, 50 from the detector assembly 24 are coupled to a suitable readout device 60, such as a chart recorder, for example, which may or may not include a signal amplifier. I

The reference gas inlet line 28 is coupled to-the inlet bore 95, to a source of diluent gas 34 such as nitrogen, for example through line 30 and metering valve 32 and to a source 40 of oxygen through line 36 and metering valve 38. i

As may be seen in FIG. 3, reference gas enters the detector assembly through the open ended tube 76 (and bore 44) andexits through the bore 44 and thence through the tube 42 to the inlet header 92.

The reference gas exit bore44 is coupled through the tube 52 and trap 54 (having valve 56 coupled thereto for trap draining purposes) to an infrared detector 58 whose output is coupled through cable 62 to a suitable readout device 64, such as a chart recorder, for example. The readout device 64 may ormay not have a signal amplifier included therein.

The reference gas usually has an inert component as well as oxygen therein. For many applications enough oxygen can be added to the inert by, as shown in FIG. 2, including a permeation tube 66 between the line 28 after it communicates with the diluent gas source 34 and point where the line 28 enters the header 26.

Referring now to FIGS. 2, 3 and 4, as well as to FIG. 1, the oxygen detector'assembly 24 includes a hollow tubular member 70 having a closed end 96 and an open end which is sealed by any suitable means to the inner end of header 26. The member 70 is a ceramic oxide tube (zirconium oxide with 7-15 percent calcium oxide, for example) with a porous platinum coating 74, 72 on the inner and outer surfaces, respectively. Electrode terminals 80, 78 are coupled to the respective coatings 74, 72, with leads 48, 50 extending through the header 26 and being coupled thereto. The reference gas exit bore communicates with the space between the tube 76 and the member 24.

Ceramic oxide cells respond to oxygen because of a flaw in their crystal structure. 'The metal ions form a perfect lattice structure, but oxygen ions do not. A large fraction of the sites that oxygen can occupy are vacant. At high temperatures the positions of the vacancies can move about. This means the negatively charged oxygen ions will also move. When there is a difference in the oxygen partial pressure between the inner and outer surfaces of the tube, electrons will flow through a circuit connecting the two surfaces. The potential, E, is given by E k T log known/[Q unknown) Where T absolute temperature [0 oxygen partial pressure a constant I Returning now to FIG. I, the combustion tube 68 contains a gas permeable catalyst bed 22 which is positioned within the heated combustion zone of the tube 68 at some distance downstream from the entry end of the tube. The distance from the catalyst bed to the entry end of the tube 68 defines a sample expansion zone within the combustion zone of the tube. For example, the heated sample expansion zone should be at least 5 cubic centimeters for an aqueous sample size of about I microliter up to microliters. Larger samples will necessitate correspondingly larger sample expansion zones.

Suitable materials for the catalyst bed include platinum, palladium, rhodium, osmium, and ruthenium. Usually these metals are obtained in the form of wire or gauze, but particulate forms thereof are also useful. Other catalysts are the particulate oxides of certain metals such as nickel and cobalt. At high enough temperatures, siliceous materials become catalytic for the purposes of the invention.

If desired, the catalytic material may be supported on a base such as asbestos or quartz fiber. In general, any combustion supporting catalyst can be used. Combustion supporting means herein that the catalyst holds oxygen in such a form that upon contact thereof with a reducing material the oxygen is available for reaction.

The catalyst bed is essentially a loosely packed bed of one or more suitable catalyst materials, or when the catalysts exist in the form of'wire or gauze, the bed is essentially a lightly compacted maze of such materials. In any event, it is sufficiently permeable to gas flow, that upon injection and vaporization of the sample to be analyzed, excessive back pressure is avoided. The length of the catalyst bed may be varied considerably, but desirably, the bed is at least about 5 centimeters long to ensure reproducible combustion.

Although the invention is not predicated upon an understanding or a theoretical explanation of the basis for operability of the invention, the following explanation of the function of the catalyst with reference to the analysis of aqueous dispersions of combustible materials, may provide basis for optimizing its performance.

It is believed that upon injection of an aqueous dispersion of combustible materials into the heated combustion zone, water vapor dilutes and envelops most of the combustible materials. Non-vaporizable materials such as inorganic refractory components of waste streams will, of course, largely remain at the site of sample vaporization. Under these conditions, gaseous oxygen within the combustion zone may not achieve sufficient contact with combustible vapors to accomplish efficient oxidation thereof for the purposes of the invention. This conclusion is substantiated by removing the catalyst bed from the combustion zone of an otherwise operable instrument. In such event, too little oxidation is observed in terms of the measured differential of oxygen content between that of the input feed gas stream, and that of the gaseous effluent containing the oxidation products. When the catalyst is present in the combustion zone, however, combustible materials gasified upon injection of the aqueous dispersion, are more effectively, if not completely oxidized by oxygen held in the catalyst bed.

Since under this hypothesis, the required oxygen is supplied from that held in the catalyst bed, the initial gaseous effluent from the combustion zone immediately after injection of the sample to be analyzed is not likely to reflect a significant decrease in oxygen content. It is not until the continually flowing feed gas stream, which sweeps the gasified combustible materials and the oxidation products thereof through the systern, is denuded of oxygen as a result of restoring the oxygen held by the catalyst bed under steady state conditions, that a significant decrease in the oxygen content occurs in the gaseous effluent from the combustion zone. If this explanation is accepted, it becomes apparent that best results under the invention will be achieved with a catalyst characterized by the ability to give up and then rapidly recover oxygen.

Aqueous dispersions of combustible materials are readily injected into the combustion zone by any one of several means. One suitable injection means is a syringe as shown in FIG. I.

The trajectory for sample injection is such that the sample will be deposited within the heating or combustion zone (the part of the combustion tube 68 lying within the furnace 12) on the upstream side of the cata lyst bed 22. The temperature of the heating or combustion zone is usually about 900 C., thus the sample and the detector assembly 24 are each subjected to this temperature during operation of the apparatus.

As the sample is inserted, a reference gas stream enters the interior of the detector assembly and then, on exiting from the detector assembly, is introduced to the combustion tube at the entry header 92. Typically the reference gas stream is nitrogen containing about 200 parts per million, by volume, of oxygen, having a constant flow rate into the combustion tube of about cubic centimeters per second (STP). As the oxygen in the combustion tube is reduced by combination with the carbon in the injected sample, the difference in the amount of oxygen in the reference gas as it leaves the combustion and contacting the outer wall surface 72 of the detector 24 tube 68 is compared with the oxygen content of the reference gas stream entering the detector assembly and contacting the layer 74 on the inner wall of the detector tube 70 cause an electrical potential to be developed between the layers 72,74. This signal is coupled by means of the leads 48, 50 to the readout device 60.

The oxygen depleted reference gas, now containing carbon dioxide, is coupled through the vent line 52, is cooled (with or without a cooling jacket around the line), through the condensate trap 54 and then through an infrared detector 58 whose output is coupled to the r d td x cefl A suitab e nfra-testslstssQtis? Beckman Model 21A analyzer, for example, equipped with a 13.3 centimeter detection all sensitized for analysis of carbon dioxide. When the infra-red detector 58 is used, the apparatus functions as a dual instrument which may be operated to determine both total oxygen content of combustible materials in aqueous systems and the total carbon content of aqueous systems.

The oxygen detector is of the Thermox type sold by Thermo-Lab Instruments, Inc. Similar detectors are sold by Westinghouse. Such detectors are discussed, for example by D. A. Sayles and J. L. Cotter in their paper entitled A New Type of Gas Sensor for Combustion Work and Metal Treating Atmospheres presented at Twentieth National ISA Iron and Steel Conference, Pittsburgh, Pa., March, 1970.

In general, the operating conditions for the apparatus of this invention as regards reference gas composition and flow conditions, the size of and type of catalyst used in the combustion tube, the heating of the combustion tube, the recording of the detector output signal, and the analytical method are as disclosed in U. S. Pat. No. 3,560,156 to Teal et al.

The inclusion of the detector cell within the combustion tube eliminates the need for a separate temperature controlled furnace, results in an apparatus which has low susceptability to contamination, is fast in response to changes in oxygen level, is easy to maintain, is insensitive to vibration, no scrubber is necessary before the combustion cell output is applied to the detector, and is economical.

The infra-red detector 58 and its conditions and manner of operation are the same as for the infra-red detector assembly in U. S. Pat. No. 3,296,435 to Teal et al.

What is claimed is:

1. Apparatus for determining the oxygen demand of combustible materials in aqueous dispersions, comprising an elongated combustion tube including a sample expansion zone, a combustion supporting catalyst dis posed in said zone and an oxygen detector extending into said zone, said tube having a closed sample and reference gas entry end and a closed exit end, means for heating said combustion tube, means at said sample entry end for introducing predetermined quantities of aqueous dispersion sample material to be analyzed, said exit end being closed by a header, said detector ex tending inwardly from said header and including a ce ramic porous Walled tube having a closed end remote from said header and a closed end at said header end thereof, said detector having electrical terminal elements contacting electrically conductive inner and outer wall surfaces of said porous tube, means for introducing reference gas containing a predetermined amount of oxygen to and withdrawing reference gas from said porous tube, means for introducing reference gas to said combustion tube through said entry end, means for withdrawing gas at said exit end, and readout means coupled to said electrical terminal elements for indicating oxygen changes appearing at said oxygen detector.

2. Apparatus in accordance with claim 8, wherein an infra-red detector assembly is coupled to said means for withdrawing gas at said exit end, thereby providing an output signal which is a function of the total carbon content of said sample.

3. Apparatus in accordance with claim 8, wherein said oxygen detector and said sample are each heated to approximately the same temperature during operation.

4. Apparatus in accordance with claim 8, wherein said means for heating said combustion tube is a tem' perature controllable furnace surrounding said tube.

5. Apparatus in accordance with claim 8, wherein said detector tube is made of a mixture comprising zirconium oxide and calcium oxide and its inner and outer wall surfaces contain a porous platinum coating.

6. Apparatus in accordance with claim 2, wherein a readout device is coupled to said infra-red detector.

7. Apparatus in accordance with claim 8, wherein said catalyst is a combustion supporting catalyst which holds oxygen available for reaction on contact with a reducing material.

8. Apparatus in accordance with claim 1, wherein said means for introducing and withdrawing reference gas from said porous tube extend through said header.

9. Apparatus in accordance with claim 1, wherein said means for withdrawing gas at said exit end extends through said header.

Po-1050 1 UNITED STATES PATENT OFFICE" CERTIFICATE OF CORRECTION Patenr No. 3,784,359 V Dated January 8 1974 in k William H. Parish It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected asshown below:

Column 2, line I 55, delete. "44" and insert --46-.

Signed and sealed this 9th day of July 1974.

(SEAL) i Attest: V V V MCCOY M. GIBSON; ,JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. Apparatus in accordance with claim 8, wherein an infra-red detector assembly is coupled to said means for withdrawing gas at said exit end, thereby providing an output signal which is a function of the total carbon content of said sample.
 3. Apparatus in accordance with claim 8, wherein said oxygen detector and said sample are each heated to approximately the same temperature during operation.
 4. Apparatus in accordance with claim 8, wherein said means for heating said combustion tube is a temperature controllable furnace surrounding said tube.
 5. Apparatus in accordance with claim 8, wherein said detector tube is made of a mixture comprising zirconium oxide and calcium oxide and its inner and outer wall surfaces contain a porous platinum coating.
 6. Apparatus in accordance with claim 2, wherein a readout device is coupled to said infra-red detector.
 7. Apparatus in accordance with claim 8, wherein said catalyst is a combustion supporting catalyst which holds oxygen available for reaction on contact with a reducing material.
 8. Apparatus in accordance with claim 1, wherein said means for introducing and withdrawing reference gas from said porous tube extend through said header.
 9. Apparatus in accordance with claim 1, wherein said means for withdrawing gas at said exit end extends through said header. 